So what's the
point?

Like many more complex techniques, the usefulness of custom collections
may not leap out at you instantly. Essentially, custom collections enable
your script to easily reach out to more than just one element on the page.

In a XML document, even the "target" attribute isn't allowed inside <a>
tags. The below script uses the ID attribute and custom collection
technique we just learned to get select links on our page to open in a new
window programmatically: